CBSE Class 12 Chapter 3 Human Reproduction
(Part-1, Male Reproductive System)
Introduction :
- Reproduction refers to the process through which living organisms produce offspring of their own kind. The reproductive system comprises organs that participate in this process.
- Humans are viviparous and reproduce sexually. However, sexual reproduction has a slower rate compared to asexual reproduction.
- Humans are unisexual, and each sex has multiple primary and secondary sex organs. Primary sex organs, also known as gonads, produce gametes, while secondary sex organs are essential for sexual reproduction but do not produce gametes.
- Gonads, such as testes in males and ovaries in females, are primary sex organs that produce gametes and secrete hormones such as testosterone and estrogen.
- Secondary sex organs are sex organs, glands, and ducts that are essential for sexual reproduction but do not produce gametes.
- Accessory, external, or secondary sex characters refer to traits that do not have a direct role in reproduction but provide specific features and structures to both sexes.
- Puberty marks the beginning of sexual maturity or the ability to reproduce. In girls, puberty occurs at the age of 10-14 years, while in boys, it occurs at the age of 13-15 years.
Male Reproductive System :
The male reproductive system is situated in the pelvic region and comprises a pair of testes and a paired duct system that includes the epididymis, vasa efferentia, vas deferens, ejaculatory duct, and urethra.
Click here Female Reproductive system (Part-2)
- The testes are located in a sac-like structure outside the abdominal cavity known as the scrotum. The scrotum helps to regulate the temperature of the testes, which is 2-2.5°C lower than the normal internal body temperature and optimal for sperm development.
- The testes are attached to the scrotum by a connective tissue band called the gubernaculum testis, and the scrotum communicates with the abdominal cavity through the inguinal canal.
- Each testis consists of about 250 compartments called testicular lobules, each containing one to three highly coiled seminiferous tubules where sperm is produced.
- The germinal epithelium, which lines each seminiferous tubule, comprises two types of cells: male germ cells (spermatogonia) and sertoli cells. Germ cells undergo spermatogenesis to form spermatozoa, while sertoli cells function as nurse cells for differentiating spermatozoa.
- The regions outside the seminiferous tubules, known as interstitial spaces, contain small blood vessels and interstitial cells or Leydig cells. Leydig cells synthesize and secrete androgens, which are testicular hormones.
Diagram : CBSE, NCERT
The male reproductive system consists of various organs and glands that work together to produce and transport semen. The process begins in the testes, where the seminiferous tubules open into the vasa efferentia through rete testis. The vasa efferentia then leave the testes and open into the epididymis located along the posterior surface of each testis.
The epididymis is responsible for temporary storage, nutrition, physiological maturation, and motility of sperms. It is divided into three parts – the anterior caput epididymis, middle corpus epididymis, and posterior cauda epididymis, where spermatozoa are concentrated and stored until ejaculation. Ejaculation is the discharge of semen due to powerful rhythmic contraction of the urethra.
The duct system conducts the semen to the exterior, beginning with the vas deferens, a large duct that arises from the cauda epididymis and reaches up to the seminal vesicle. The ejaculatory ducts are short straight muscular tubes that are formed by the union of the vas deferens and the duct of the seminal vesicle. They have a contractile mechanism that aids in the emission of seminal fluid.
The urethra leads from the urinary bladder through the prostate gland and into the penis. It has four parts – the urinary, prostatic, membranous, and penile – with the latter two forming the outflow pathway for the urine and the seminal fluid. The penis is the male copulatory organ, with the glans penis being the tip that is highly sensitive to stimulation. The prepuce is a loose retractile foreskin that covers the glans penis.
Click here Female Reproductive system (Part-2)
The seminal plasma is composed of secretions from the seminal vesicles, prostate, and paired bulbourethral glands. It is rich in fructose, calcium, and certain enzymes.
The secretions of the bulbourethral glands also help in the lubrication of the penis. The seminal vesicles are long pouches with a muscular wall that secrete spermatozoa activating substances, such as fructose, citrate, inositol, prostaglandins, and several proteins. Sperms use fructose as a respiratory substrate, and the seminal fluid maintains their viability and motility.
The seminal vesicle secretes an alkaline, nutritive fluid that forms the main part, i.e., 60% of the semen. It is also called the uterus masculinus.
The seminal vesicles are located between the bladder and rectum. They secrete a fluid that constitutes about 60% of the semen and contains fructose, citrate, inositol, prostaglandins, and several proteins. The secretions of the seminal vesicles activate and nourish the spermatozoa and help in maintaining their viability and motility.
Click here Female Reproductive system (Part-2)
The prostate gland surrounds the first portion of the urethra and secretes a slightly acidic fluid (pH about 6.5) that makes up about 25% of the semen. This fluid contains citric acid, calcium, phosphate, fibrinogen, and fibrinolysin. The secretion of the prostate gland combines with the secretion of seminal vesicles, causing the semen to coagulate. This coagulated semen reduces the mobility of the sperms, conserving their energy. After some time, due to the action of fibrinolysins, the semen liquefies, allowing the sperms to move freely.
The Cowper’s glands, also called Bulbourethral glands, are a pair of glands attached to the urethra. They secrete alkaline mucus that is discharged into the spongy part of the urethra. The mucus lubricates the reproductive tract and neutralizes any remaining urine acidity. The secretion of Cowper’s glands is produced before the ejaculation of semen and may carry some spermatozoa released before ejaculation, which is one of the reasons for the high failure rate of the withdrawal method of birth control.
Hormonal Control Over Male Reproductive System :
The production of testosterone hormone in Leydig’s cells of the testis is stimulated by Luteinizing Hormone (LH) of the anterior pituitary gland. Testosterone hormone is responsible for the development and maintenance of primary and secondary sexual characteristics in males, including the growth and function of the prostate gland, seminal vesicles, and bulbourethral glands. It also regulates spermatogenesis in the seminiferous tubules.
FSH, also secreted by the anterior pituitary gland, stimulates the Sertoli cells of the seminiferous tubules, which support and nourish the developing sperm cells. FSH also plays a role in regulating spermatogenesis.
ICSH, another hormone secreted by the anterior pituitary gland, acts on the Leydig’s cells of the testis to stimulate the production of testosterone hormone.
The secretion of LH, FSH, and ICSH is regulated by gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus. GnRH stimulates the release of LH and FSH from the anterior pituitary gland, which in turn stimulate the Leydig’s cells and Sertoli cells respectively to produce testosterone and support spermatogenesis.